Video File Size Calculator

Enter a video's bitrate in megabits per second and its running time in minutes, and the calculator estimates the finished file size in both gigabytes and megabytes. It is the quick check worth doing before you record a long clip, queue an upload, or decide whether a memory card has room. Everything updates as you type and stays in the browser.

How the size is worked out

Bitrate is a count of bits stored for every second of video, so file size is that rate multiplied by the number of seconds, then converted from bits to bytes by dividing by eight.

bytes = bitrate × 10⁶ × minutes × 60 ÷ 8

Take the defaults: 8 Mbps over 42 minutes. Eight megabits is 8,000,000 bits per second, and 42 minutes is 2,520 seconds, so the clip holds 8,000,000 × 2,520 = 20,160,000,000 bits. Divide by eight and that is 2,520,000,000 bytes, or 2.52 GB, which is also 2,520 MB. The gigabyte here is the decimal one drive makers use, where 1 GB is 1,000 MB, so a 2.52 GB file really does claim 2.52 GB of a card's printed capacity.

The bit and the byte

Every figure this tool produces rests on two units older than digital video by decades. The bit, a contraction of binary digit, is the smallest unit of information, a single choice between two states. The mathematician John Tukey coined that contraction in a Bell Labs memo dated 9 January 1947, and Claude Shannon gave the unit its lasting definition in A Mathematical Theory of Communication, published in the Bell System Technical Journal in July and October 1948. That paper founded information theory, and it credits the word itself to J. W. Tukey. The byte came later. Werner Buchholz coined it in June 1956 while designing the IBM 7030 Stretch, IBM's first transistorised supercomputer, and respelled bite with a y on purpose so it would not be misread as bit. On Stretch a byte was anything from one to eight bits; IBM fixed it at eight when it announced the System/360 in April 1964, and eight it has stayed. That is why the division by eight closes the formula: bitrate is quoted in bits, storage is sold in bytes, and eight bits make one byte.

How codecs decide the bitrate

Raw, uncompressed video would be far too large to store or stream. A single 1080p frame holds about two million pixels, each carrying colour, and video runs 24 to 60 of those frames every second; left uncompressed at 30 frames a second in the usual eight-bit sampling, that stream runs to roughly 750 megabits per second. The reason a two-hour film fits on a disc is a mathematical method published in 1974 by Nasir Ahmed, T. Natarajan and K. R. Rao, and proposed by Ahmed around 1972: the discrete cosine transform, or DCT. It rewrites a block of pixels as a sum of wave patterns, letting an encoder keep the coarse shapes the eye notices and throw away fine detail it does not. Almost every image and video format since, from JPEG through MPEG and the whole H.26x family, is built on it.

The first practical video standard to use these ideas was H.261, ratified in 1988 by the CCITT, now the ITU-T, for video calls over ISDN lines. It put into standard practice the split between full frames and difference frames that still governs bitrate: an encoder stores one complete picture, then records only what changes in the frames that follow. Motion in the scene means more change, and more change means more bits. The lineage grew steadily, through MPEG-1 in 1993 for the Video CD, MPEG-2 in 1995 for the DVD and digital television, H.264 in 2003 for streaming and Blu-ray, HEVC in 2013, and the royalty-free AV1 in 2018. Each generation cut the bitrate needed for a given picture. HEVC was designed to match H.264 quality at about half the bitrate, and published comparisons put the saving actually achieved somewhere between 25 and 50 percent depending on the footage, which is why the same film can look identical in a smaller file on a newer codec. The calculator does not need to know which codec made the file. Whatever the encoder chose, the bitrate it settled on is the single number that fixes the size, and that is what you enter.

Typical bitrates to plug in

If you do not know the exact bitrate, these ranges cover most real footage:

Recording bitrates split sharply by codec. The same handset writing 4K at 30 frames a second uses roughly 25 Mbps in HEVC and close to 50 Mbps in H.264, so check the camera's format setting before trusting either end of that row. Resolution matters far less than bitrate. A heavily compressed 4K stream can be smaller than a lightly compressed 1080p one, so the megabits figure is what actually sets the size.

Audio and variable bitrate

The calculator treats the whole bitrate as video, which is close enough because sound is a small slice. Stereo AAC audio runs about 128 to 256 kbps, so on a 5 Mbps stream the soundtrack is only about 2.5 to 5 percent of the file, and if you enter the combined bitrate it is already counted.

The bigger source of drift is variable bitrate. Most encoders — H.264, HEVC and AV1 — spend more bits on fast, detailed scenes and fewer on still ones, so the figure you type is really an average. A two-hour film can finish 10 to 20 percent either side of a flat estimate depending on how busy the footage is. Constant bitrate, still common for live streaming, tracks this math almost exactly.

Reading the result on different systems

The size shown here uses decimal units, the same ones storage is sold in worldwide, so it is not a number that shifts between the US, UK, EU, Canada or Australia. Your operating system may disagree with the label, though. Windows reports the same 2.52 GB file as roughly 2.35 "GB" because it counts in binary gibibytes while keeping the GB name, whereas macOS and most Linux file managers show 2.52 GB and match this calculator. The count of bytes is identical either way.

The clash goes back to a naming decision the industry never fully settled. For years a kilobyte meant 1,024 bytes to programmers and 1,000 bytes to drive makers. In January 1999 the International Electrotechnical Commission tried to end the ambiguity, publishing Amendment 2 to IEC 60027-2, which named the binary sizes kibibyte, mebibyte and gibibyte and reserved kilo, mega and giga for the decimal powers of 1,000. Storage manufacturers took the decimal meaning while Windows kept the binary sizes under the old names. This calculator follows the decimal convention, which is why its gigabyte matches the number printed on the card.

Frequently asked questions

How big is a 1-hour 1080p video?

At a typical streaming bitrate of 5 to 8 Mbps, one hour of 1080p runs about 2.25 to 3.6 GB. Taking 6 Mbps as a middle figure, 6 × 1,000,000 × 3,600 ÷ 8 is 2,700,000,000 bytes, or 2.7 GB. A phone recording that same hour in 4K can produce ten times as much.

How do I convert Mbps to GB per minute?

One megabit per second stores 60 megabits, which is 7.5 MB, every minute, because 60 ÷ 8 is 7.5. So multiply your bitrate in Mbps by 7.5 for MB per minute, or by 0.0075 for GB per minute. At 8 Mbps that is 60 MB a minute, which is why the defaults reach 2.52 GB over 42 minutes.

Does higher resolution always mean a bigger file?

Not on its own. File size is set by bitrate, not pixel count, so a 4K clip encoded at 8 Mbps is the same size as a 1080p clip at 8 Mbps. Higher resolutions usually carry higher bitrates to stay sharp, and that is the real reason 4K files are large. Compress 4K hard enough and it can be smaller than a generous 1080p export.

Why is my recorded video bigger than this estimate?

Phone and camera recordings often use very high bitrates: 4K at 60fps can exceed 90 Mbps, roughly ten times a streaming clip, so a few minutes fills hundreds of megabytes. Variable bitrate also pushes busy, high-motion footage above the average you entered. Enter the camera's actual recording bitrate from its settings rather than a streaming figure for a closer match.

Is a 25 GB Blu-ray enough for a 2-hour movie?

A single-layer Blu-ray holds 25 GB, and a 2-hour film at 25 Mbps works out to 25 × 1,000,000 × 7,200 ÷ 8, which is 22,500,000,000 bytes, about 22.5 GB, so it fits with a little room to spare. Dual-layer discs hold 50 GB for higher bitrates or longer films. Streaming versions of the same film are far smaller because they use only 5 to 8 Mbps.